Probability of males to outlive females: an international comparison from 1751 to 2020

Probability of males to outlive females: an international comparison from 1751 to 2020. Marie-Pier Bergeron-Boucher et al. BMJ Open, Volume 12, Issue 8, Aug 2022. https://bmjopen.bmj.com/content/12/8/e059964

Abstract

Objective To measure sex differences in lifespan based on the probability of males to outlive females.

Design International comparison of national and regional sex-specific life tables from the Human Mortality Database and the World Population Prospects.

Setting 199 populations spanning all continents, between 1751 and 2020.

Primary outcome measure We used the outsurvival statistic ( φ ) to measure inequality in lifespan between sexes, which is interpreted here as the probability of males to outlive females.

Results In random pairs of one male and one female at age 0, the probability of the male outliving the female varies between 25% and 50% for life tables in almost all years since 1751 and across almost all populations. We show that φ is negatively correlated with sex differences in life expectancy and positively correlated with the level of lifespan variation. The important reduction of lifespan inequality observed in recent years has made it less likely for a male to outlive a female.

Conclusions Although male life expectancy is generally lower than female life expectancy, and male death rates are usually higher at all ages, males have a substantial chance of outliving females. These findings challenge the general impression that ‘men do not live as long as women’ and reveal a more nuanced inequality in lifespans between females and males.

Discussion

Our study reveals a nuanced inequality in lifespan between females and males, with between one and two men out of four outliving a randomly paired woman in almost all points in time across 199 populations. These results complement the picture given by the comparisons based on life expectancy, which is a summary measure with no information on variation. A blind interpretation of life expectancy differences can sometimes lead to a distorted perception of the actual inequalities. Not all females outlive males, even if a majority do. But the minority that do not is not small. For example, a sex difference in life expectancy at birth of 10 years can be associated with a probability of males outliving females as high as 40%, indicating that 40% of males have a longer lifespan than that of a randomly paired female. Not all males have a disadvantage of 10 years, which is overlooked by solely making comparisons of life expectancy. However, a small number of males will live very short lives to result in that difference. For example, more baby boys die than baby girls in most countries.

The length of the lifespan of an individual results from a complex combination of biological, environmental and behavioural factors. Being male or female does impact lifespan, but it is not the only determinant contributing to inequalities. Lifespan has been shown to be influenced by marital status, income, education, race/ethnicity, urban/rural residence, etc.33 As we only disaggregated the population by sex and because of this complex interaction, lifespan distributions of females and males overlap. This nuance is captured by the φ metric. Males with a lower education level or who are unmarried have a particularly low chance of outliving a female. But males with a university degree or who are married have a higher chance of outliving females, in particular females with a lower education level and who are single.

As previously discussed, the φ metric expresses the probability of males to outlive females among randomly paired individuals, assuming independence between populations. However, males and females in a population are generally not random pairs but often couples, whose health and mortality have been found to be positively correlated due to a strong effect of social ties on health and longevity.34 Coupled individuals also influence each other’s health,35 and this is particularly true for males, who benefit more than females from being in a stable relationship.36 The datasets used for the analysis do not permit the estimation of the probability of males outliving females for non-randomly paired individuals. However, the outsurvival statistic relates to the probability of the husbands to outlive their wives, and even though such a measure accounts for the difference in age between husband and wife, it has been shown generally to be between 30% and 40%,37–39 values that are quite close to φ .

Other measures of overlap and distance between distributions could have been used. In the online supplemental materials, we compare the outsurvival statistic with a stratification index used by Shi and colleagues20 and the KL divergence. We found that all three indicators are strongly correlated and using any one of these would not have changed the general conclusions from this article. However, unlike the other indicators, φ directly indicates when males live longer than females, which we found in a few instances.

Trends over time in φ are consistent with the reversed trends in sex differences in life expectancy40: in developed countries, the probability of males outliving females decreased until the 1970s, after which it gradually increased in all populations. Studies showed that the increase in sex differences in mortality emerged in cohorts born after 1880,10 41 which is consistent with our analysis of φ (see online supplemental materials). The increase and decrease in sex differences in life expectancy were mainly attributed to the smoking epidemic and other behavioural differences between sexes.7 13 42

The φ values are generally higher in low/middle-income countries. However, this should not be interpreted as a sign of greater gender equality in survival. Southern Asian countries had very high φ values, above 50% in the 1950s and 1960s. Studies for India showed that mortality below age 5 was higher for females than males and remained higher for females in recent years.43 44 However, females had a growing mortality advantage above age 15 years since the 1980s, ‘balancing out’ the disadvantage at younger ages. The reasons for the higher φ and decreasing trends in developing regions vary across countries. It is outside the scope of this study to provide a detailed explanation for the trends in each country.

The outsurvival statistic can be informative for public health interventions.21 Governments develop public health programmes to reduce lifespan inequalities at different levels (eg, socioeconomic status, race, sex, etc). It would be misleading to say that half of the population is disadvantaged by sex differences in lifespan. The inequalities are more nuanced. If 40% of males live longer than females, it could be argued that if a policy aiming at reducing inequalities between sexes targeted the full male population, some of the efforts and investments would be misallocated. Such a policy could be more efficient if φ approaches 0, indicating that sex would explain a large part of the lifespan inequalities within the population, whereas a φ closer to 0.5 indicates that other characteristics (eg, socioeconomic and marital statuses) are involved in creating inequalities. We showed that some subpopulations of males have a high probability (above 50%) of outliving some subpopulations of females. Males who are married or have a university degree tend to outlive females who are unmarried or do not have a high school diploma. Inequalities in lifespan between sexes are attributable to some individuals within each population and not to the whole population. Indeed, Luy and Gast12 found that male excess mortality is mainly caused by some specific subpopulations of males with particularly high mortality. Being able to better identify the characteristics of the short-lived men could more efficiently help tackle male–female inequality.

An important result of our analysis is that the smaller the SD in the age at death, the smaller the φ . The reduction of lifespan inequality observed over time has then made it less likely for males to outlive females. This is partly explained by the fact that lifespan variation reduction has been driven by mortality declines at younger ages.45 When looking at the lifespan distribution (as in figure 1, scenario D), survival improvements at younger ages narrowed the left tails of the distribution for both sexes. By reducing the left tail of female distribution, without increasing the right tail of the male distribution, the overlapping area is reduced. In other words, the number of females with shorter lifespan, easier to outlive, decreased over time. Indeed, it has been shown that mortality declined at a faster pace for females than males below age 50, especially in the first half of the 20th century.46 47 This finding implies that more efforts are required today than in the past to reduce these inequalities, for a same difference in life expectancy. While inequalities were mainly attributable to infant and child mortality, they are today increasingly attributable to older and broader age groups. Men maintained their disadvantage at younger ages, but also faced an increasing disadvantage at older ages. Men are more prone to accidents and homicides in their 20s and 30s than females, and they tend to smoke and drink more leading to higher cancer prevalence and death in their 60s. At the same time, women benefited from reduced maternal mortality and recorded faster mortality decline at older ages. Efforts in reducing lifespan inequalities must thus target diverse factors, causes and ages.13 46 48

A decrease of φ might indicate a discrepancy in the causes of death that affect males and females. External mortality due to accidents and suicide has become more relevant in shaping sex differences in survival in recent years in high-income populations.12 Another example is observed in Latin American populations, where homicides and violent deaths have had an increased burden among males in comparison with females since the 1990s.49 50 In Mexico, for example, the increase in homicide mortality, especially among men between 20 and 40 years, contributed to increasing the gap in mortality between females and males.51 This phenomenon is reflected in the decrease over time in the overlapping of lifespan distributions, directly informing healthcare systems of emerging inequalities.

However, one might ask if a wider overlapping is necessarily better for healthcare systems. On the one hand, a larger overlapping means less inequality between sexes, but on its own it does not ensure that there is more ‘health justice’. For example, if the overlapping areas are large, this still shows a situation of great uncertainty in lifespan for both groups. One health evaluator actor could even prefer a situation where there is a small gap between groups but less inequality within the groups. In the case of sex differences, there might always be between-group differences due to biological factors,2 52 but more health equity could be reached by reducing within-group inequalities. We argue that the outsurvival statistic is a new tool to evaluate health inequalities between groups within a population by uncovering underlying dynamics that are otherwise hidden when looking only at conventional indicators. Therefore, it can inform healthcare systems of the subsequent directions to reach the preferred goal.

 

If children with low socio-economic level parents were to grow up in counties with economic connectedness comparable to that of the average child with high level parents, their incomes in adulthood would increase by 20% on average

Social Capital I: Measurement and Associations with Economic Mobility. Raj Chetty, Matthew O. Jackson, Theresa Kuchler, Johannes Stroebel, Nathaniel Hendren, Robert B. Fluegge, Sara Gong, Federico González. NBER Working Paper 30313. July 2022. DOI 10.3386/w30313

Abstract: In this paper—the first in a series of two papers that use data on 21 billion friendships from Facebook to study social capital—we measure and analyze three types of social capital by ZIP code in the United States: (i) connectedness between different types of people, such as those with low vs. high socioeconomic status (SES); (ii) social cohesion, such as the extent of cliques in friendship networks; and (iii) civic engagement, such as rates of volunteering. These measures vary substantially across areas, but are not highly correlated with each other. We demonstrate the importance of distinguishing these forms of social capital by analyzing their associations with economic mobility across areas. The fraction of high-SES friends among low-SES individuals—which we term economic connectedness—is among the strongest predictors of upward income mobility identified to date, whereas other social capital measures are not strongly associated with economic mobility. If children with low-SES parents were to grow up in counties with economic connectedness comparable to that of the average child with high-SES parents, their incomes in adulthood would increase by 20% on average. Differences in economic connectedness can explain well-known relationships between upward income mobility and racial segregation, poverty rates, and inequality. To support further research and policy interventions, we publicly release privacy-protected statistics on social capital by ZIP code at www.socialcapital.org.

Social Capital II: Determinants of Economic Connectedness. Raj Chetty, Matthew O. Jackson, Theresa Kuchler, Johannes Stroebel, Nathaniel Hendren, Robert B. Fluegge, Sara Gong, Federico Gonzalez. NBER Working Paper 30314. July 2022, revised August 2022. DOI 10.3386/w30314

Abstract: Low levels of social interaction across class lines have generated widespread concern and are associated with worse outcomes, such as lower rates of upward income mobility. Here, we analyze the determinants of cross-class interaction using data from Facebook, building upon the analysis in the first paper in this series. We show that about half of the social disconnection across socioeconomic lines—measured as the difference in the share of high-socioeconomic status (SES) friends between low- and high-SES people—is explained by differences in exposure to high- SES people in groups such as schools and religious organizations. The other half is explained by friending bias—the tendency for low-SES people to befriend high-SES people at lower rates even conditional on exposure. Friending bias is shaped by the structure of the groups in which people interact. For example, friending bias is higher in larger and more diverse groups and lower in religious organizations than in schools and workplaces. Distinguishing exposure from friending bias is helpful for identifying interventions to increase cross-SES friendships (economic connectedness). Using fluctuations in the share of high-SES students across high school cohorts, we show that increases in high-SES exposure lead low-SES people to form more friendships with high-SES people in schools that exhibit low levels of friending bias. Hence, socioeconomic integration can increase economic connectedness in communities where friending bias is low. In contrast, when friending bias is high, increasing cross-SES interaction among existing members may be necessary to increase economic connectedness. To support such efforts, we release privacy-protected statistics on economic connectedness, exposure, and friending bias for each ZIP code, high school, and college in the U.S. at www.socialcapital.org.

How does early menopause and menopause symptoms affect women’s careers? The conservative estimate of the cost of early menopause for a woman is £20k, while the cost of suffering an average level of menopause symptoms is £10k

The consequences of early menopause and menopause symptoms for labour market participation. Alex Bryson et al. Social Science & Medicine, Volume 293, January 2022, 114676. https://doi.org/10.1016/j.socscimed.2021.114676

Highlights

• Early natural menopause substantially reduces employment rates among women.

• The number of menopause symptoms women face is also associated with lower employment rates.

• These effects are larger for symptoms which women say “bother me a lot”.

• Psychological problems due to menopause are associated with the biggest employment effects.

Popular version: How does early menopause and menopause symptoms affect women’s careers? Mar 8 2022. https://blog.ukdataservice.ac.uk/how-does-early-menopause-and-menopause-symptoms-affect-womens-careers

Abstract: Using a difference-in-difference estimator we identify the causal impact of early menopause and menopause symptoms on the time women spend in employment through to their mid-50s. We find the onset of early natural menopause (before age 45) reduces months spent in employment by 9 percentage points once women enter their 50s compared with women who do not experience early menopause. Early menopause is not associated with a difference in full-time employment rates. The number of menopause symptoms women face at age 50 is associated with lower employment rates: each additional symptom lowers employment rates and full-time employment rates by around half a percentage point. But not all symptoms have the same effects. Vasomotor symptoms tend not to be associated with lower employment rates, whereas the employment of women who suffer psychological problems due to menopause is adversely affected. Every additional psychological problem associated with menopause reduces employment and full-time employment rates by 1–2 percentage points, rising to 2–4 percentage points when those symptoms are reported as particularly bothersome.

Keywords: MenopauseEarly menopauseMenopausal symptomsVasomotor symptomsEmploymentFull-time employmentBirth cohort

5. Conclusions

Our paper is the first to estimate the effects of early menopause and menopausal symptoms on employment and full-time employment rates among women. We exploit prospective birth cohort data for all women born in a particular week in 1958 to estimate the causal effects of menopause on employment rates using a difference-in-difference strategy. This technique compares the gap in employment rates during their 20s and early 30s with the employment gap in their 50s for women who went onto experience early menopause versus those who did not. We make similar comparisons between women according to the intensity with which they experienced menopausal symptoms when aged 50. In doing so we control for a rich array of variables collected at birth, in childhood, and in early adulthood which can affect employment prospects and experiences of menopause. We show employment and full-time employment trends during their 20s and early 30s did not differ significantly between the ‘treated’ group – those who went on to experience early menopause or more menopausal symptoms – and their ‘control’ groups who did not experience early menopause or did not suffer many menopausal symptoms. This provides some assurance that their employment rates may have trended in similar fashions later in their lives if they had not experienced menopause differently.

We find women's employment rates, and their full-time employment rates fall as the number of menopausal symptoms they report rises. Effects are larger for symptoms that are reported as ‘bothersome’. The effects are quantitatively large. For instance, a woman who experiences the mean number of menopausal symptoms at age 50 can expect to have an employment rate in her 50s that is 4 percentage points lower than a woman who has no menopausal symptoms.

Different types of menopause symptom have different employment effects. For instance, vasomotor symptoms do not affect full-time employment rates, and they only affect employment rates where they are considered ‘bothersome’. In contrast, psychological health problems associated with menopause significantly lower employment and full-time employment rates, and effects are much larger when those symptoms are ‘bothersome’.

Early menopause is associated with a very large (9 percentage point) reduction in employment rates once women reach their 50s, yet it has no statistically significant effect on women's full-time employment rates. It is unclear why early menopause should affect employment rates, but not full-time employment rates. This issue is worthy of further investigation.

It is striking that the inclusion and exclusion of potential confounders makes very little difference to the impact of early menopause and menopause symptoms on employment and full-time employment rates. Even though their inclusion increases the variance in employment rates explained by our models (as indicated by the adjusted R-squared) the coefficient and statistical significance of the interaction capturing the impact of menopause are nearly identical in all cases. Following Oster (2019) we take coefficient stability in the face of adjustments to conditioning covariates as an indication that results are unlikely to be biased by omitted variables.

There are some limitations to this study. First, although women are asked specifically to identify health-related symptoms due to the menopause, in some cases those symptoms may be due to other changes women are going through at the same time which are not directly linked to the menopause. Second, our data only collect information on symptoms related to menopause in the year leading up to the survey interview at age 50. Some women may have experienced symptoms earlier which did not persist to age 50, leading to some error in our ability to accurately capture symptoms related to menopause. Some women who experienced symptoms, but not at age 50, will be misclassified as having no symptoms. However, assuming symptoms experienced earlier than age 50 also have a detrimental impact on employment, this will mean our estimates of symptoms’ effects on employment are downwardly biased. Third, it is worth recalling that the Great Recession hit when the women in the study reached age 50. This was a very severe recession creating what were, at the time, unprecedented labour market problems for many. It would be valuable to see whether our results are replicated in more benign labour market conditions.

These negative employment effects of early menopause and menopausal symptoms are cause for some concern, not only because the size of the effects is large, but also because so many women suffer these problems. As we have shown, the mean number of menopausal symptoms experienced by women in this birth cohort when aged 50 was 8, including 2 particularly ‘bothersome’ symptoms. Five percent of women in the estimation sample had experienced early menopause.

These employment effects of early menopause and menopause symptoms add to the personal costs they have for women suffering from them in terms of their physical and mental health, and potentially their effects on women's private lives, although we do not quantify them here. They also have costs for society, in terms of the health care costs of treating women's symptoms, potential productivity losses from women's lost hours of work and ability to work productively. It is conceivable that they will also affect women's retirement decisions and thus pension entitlements.

Having identified the size and extent of the problem government and employers should consider steps that could be taken to ameliorate the problems women face in their working lives due to the menopause. That said, this is the first study of its kind, so there is value in seeking to replicate and extend research investigating the impact of early menopause and menopausal symptoms on labour market outcomes. First, it would be valuable to know whether the effects we identify might vary for other cohorts of women including more recent entrants to the labour market. Second, there would be value exploring the heterogeneity of menopausal effects and whether there are aspects of women's experiences that may ameliorate the effects of menopause. For instance, it may be that women are better able to manage menopause symptoms where they have greater opportunities to manage working patterns or working hours, as might be the case among self-employed women or employees in workplaces with policies and practices expressly intended to assist women affected by menopause. Third, we know very little about the effects of early menopause and menopausal symptoms on other aspects of women's labour market experiences. We would have a better picture if studies were undertaken to investigate the impacts of menopause on women's wellbeing at work, their job satisfaction and their earnings. Finally, we know of no studies piloting policies or practices in the workplace that might assist women in raising health-related problems they may have during menopause, nor in coping with those problems. These evaluations are needed to provide the evidence base employers and government need so they know what actions to take to improve women's working lives.

Men, particularly those who declare being interested in politics, take longer than women to admit that they do not know the answer to political knowledge items

How long does it take to admit that you do not know? Gender differences in response time to political knowledge questions. Mónica Ferrín, Gema García-Albacete, Irene Sánchez-Vítores. Research & Politics, August 5, 2022. https://doi.org/10.1177/20531680221117454

Abstract: The implications of the persistent gender gap in political knowledge are a puzzle that the literature is still disentangling; and research has evidenced important differences in the way women and men respond to survey questions. We argue in this article that political knowledge survey items not only inform about differences in cognition but also about other latent traits related to gender stereotyping. Gender stereotypes around political knowledge push men to be knowledgeable but not so much women, which we expect to affect men and women’s survey responses differently. To test this expectation, we explore response times of do not know answers to political knowledge items. Our results show that men, particularly those who declare being interested in politics, take longer than women to admit that they do not know the answer to political knowledge items.

Keywords: political knowledge, do not know, gender gap, response time, stereotypes

Final remarks

This article contributes to the literature on gender and politics by showing that gender-conformity affects both men and women. Our interpretation of the longer time men take to respond DK is that men are gender stereotyped to be politically knowledgeable. As a consequence, they are reluctant to verbalize their lack of knowledge, which implies that they take as much time as possible before yielding and admitting they do not know the answer.

While some authors have argued that do not know answers simply reflect ignorance on behalf of respondents, regardless of the question format or their personality traits (Jessee, 2017; Luskin and Bullock, 2011), this article shows that DK responses do not distribute randomly. Gender differences in DK response latencies provide an additional piece of evidence regarding the effects of stereotype threat on respondents (Davis and Silver, 2003; Pereira, 2019) and how it results in a further overestimation of men’s actual levels of political knowledge, compared to women’s. Further research should explore the extent to which priming other social identities (McGlone et al., 2006; Shih et al., 1999), amongst other strategies, could enhance respondent’s confidence and provide more accurate depiction of what they know about politics.

This article also opens an avenue for further research on survey methodology. We have shown that response latencies of do not know answers hide differentiated traits for women and men, based on gender stereotypes. To date, little research has explored the potential interpretation of groups’ differences in response times in relation to data quality and comparability. We offer here evidence that response times differ significantly between women and men, which implies different reactions to survey items. This finding should encourage the use of response latencies as a tool to explore heterogeneity in responses to survey items.

In contrast to many other growth models we find that the taxation of human capital has a substantial negative effect on its accumulation; this in turn reduces innovation and, consequently, the income growth rate

Human capital, innovation, and growth. Clas Eriksson, Johan Lindén, Christos Papahristodoulou. International Journal of Economic Theory, May 16 2022. https://doi.org/10.1111/ijet.12346

Abstract: This paper explores the interaction between human capital and innovation in the process of economic growth. Using a model of endogenous growth, we focus on how taxes and other policy instruments affect the incentives to invest in human capital. In contrast to many other growth models we find that the taxation of human capital has a substantial negative effect on its accumulation. This in turn reduces innovation and, consequently, the income growth rate. More surprisingly, other policies that are intended to stimulate growth may have opposing effects on innovation and the accumulation of human capital. For example, while subsidies to research and to intermediate inputs do have positive effects on innovation and growth, they lead to a lower stock of human capital, in the empirically relevant case when the elasticity of intertemporal substitution in consumption is low.

6 CONCLUSIONS

Human capital and innovation are important drivers of economic growth. This paper explores a model in which both the acquirement of human capital and innovation are endogenous, and where a share of the human capital is used in research. We examine the incentives to undertake research and spend time in schooling, in particular with respect to the role of economic policy for those growth-promoting activities.

We develop a model similar to Romer (1990), with the important difference that human capital is endogenous. In addition, contrary to the simpler standard formulation in many other growth models where labor taxes drop out of the equations, our household's optimization implies that the taxation on human capital has a substantial negative effect on the formation of this factor. Since human capital is an essential input in research, this in turn lowers the income growth rate. Similarly, if the tax on unskilled labor is higher, more time will be spent in schooling to build human capital, resulting in a higher growth rate.

While subsidies to research and to intermediate inputs have positive effects on growth, they do not necessarily lead to a larger long-run stock of human capital in the economy. If the elasticity of intertemporal substitution in consumption is sufficiently low, these policy instruments stimulate growth by inducing a reallocation of a smaller stock of human capital toward more research.

An economy which taxes interest income at a higher rate will experience lower growth, because the representative household decides to shift some consumption from the future to the present in response to the lower net interest rate. The total stock of human capital is lower on the BGP and the relative wage increases.

Our model implies a substantial negative tax effect on economic growth. The analysis thus indicates that the design of the tax system may be important for the rate of growth in an economy. This theoretical finding is consistent with some important recent empirical research.

Impression formation at zero-acquaintance: Penises which were wider, longer, and moderately hairy were perceived more positively in terms of personality and sexual appeal; shorter and narrower penises were perceived as more neurotic

Personality and Sexual Perceptions of Penises: Digital Impression Formation. Thomas R. Brooks & Stephen Reysen. Sexuality & Culture, Aug 4 2022. https://rd.springer.com/article/10.1007/s12119-022-10000-y

Abstract: Dating app users are likely to experience a high frequency of viewing the sexually explicit material of potential partners prior to a physical meeting. The present study aimed to investigate what information is inferred from a picture of a penis at zero-acquaintance. Past research in impression formation at zero-acquaintance has demonstrated a stability with regard to personality and trait perceptions of faces. Utilizing 106 participants, our study extends this paradigm by testing the hypothesis that penis prototypicality would be associated with attractiveness, as well as explore the personality and sexual perceptions of penises along the dimensions of girth, length, and amount of pubic hair. The hypotheses were confirmed and the analysis of penis dimensions revealed strong results. Penises which were wider, longer, and moderately hairy were perceived more positively in terms of personality and sexual appeal. Shorter and narrower penises were perceived as more neurotic. The results demonstrate the function of impression formation within the digital sexual landscape with regard to sexually explicit material.

Free-ranging long-tailed macaques: Do monkeys use sex toys? Evidence of stone tool-assisted masturbation.

Do monkeys use sex toys? Evidence of stone tool-assisted masturbation in free-ranging long-tailed macaques. Camilla Cenni,Jessica B. A. Christie, Yanni Van der Pant, Noëlle Gunst, Paul L. Vasey, I Nengah Wandia, Jean-Baptiste Leca. Ethology, August 4 2022. https://doi.org/10.1111/eth.13324

Abstract: Recent reports on tool use in nonforaging contexts have led researchers to reconsider the proximate drivers of instrumental object manipulation. In this study, we explore the physiological and behavioral correlates of two stone-directed and seemingly playful actions, the repetitive tapping and rubbing of stones onto the genital and inguinal area, respectively, that may have been co-opted into self-directed tool-assisted masturbation in long-tailed macaques (i.e., “Sex Toy” hypothesis). We predicted that genital and inguinal stone-tapping and rubbing would be more closely temporally associated with physiological responses (e.g., estrus in females, penile erection in males) and behavior patterns (e.g., sexual mounts and other mating interactions) that are sexually motivated than other stone-directed play. We also predicted that the stones selected to perform genital and inguinal stone-tapping and rubbing actions would be less variable in number, size, and texture than the stones typically used during other stone-directed playful actions. Overall, our data partly supported the “Sex Toy” hypothesis indicating that stone-directed tapping and rubbing onto the genital and inguinal area are sexually motivated behaviors. Our research suggests that instrumental behaviors of questionably adaptive value may be maintained over evolutionary time through pleasurable/self-rewarding mechanisms, such as those underlying playful and sexual activities.

Naturism & Casual Stripping Predict Social Body Appreciation & less social physique anxiety; sexting predicts social physique anxiety in men

Good Nudes and Bad Nudes: How Naturism, Casual Stripping, and Sexting Predict Social Physique Anxiety and Body Appreciation. Keon West & Eliza Kukawska. Sexuality & Culture, Aug 5 2022. https://rd.springer.com/article/10.1007/s12119-022-09990-6

Abstract: Prior research suggests that naturism leads to less social physique anxiety and more positive body image, but that other forms of public nudity (e.g., casual stripping, sexting) may be harmful, particularly for women. Two cross-sectional studies built on those previous findings. Study 1 (N1 = 6670) found a positive relationship between generalised nude activity and body appreciation which was not moderated by gender. Study 2 (N2 = 331) found that both naturism and casual stripping predicted more body appreciation, a relationship mediated by less social physique anxiety. Again, these relationships were not moderated by gender. In contrast, sexting did not predict body appreciation and predicted more social physique anxiety, but only in men. These findings highlight that some types of nudity may be more beneficial or harmful than others, and that future research and policy should specify the type of nudity under consideration in order to maximise positive effects.

General Discussion

These two studies replicated, clarified, and built on previous findings concerning nudity and psychological outcomes. Using a large, age-diverse and gender-diverse sample, Study 1 found that participation in public nudity generally predicted more positive body image (i.e., higher levels of body appreciation). Furthermore, the lack of moderation by gender, despite the substantial sample size in that study, is a strong indicator that this moderation may be very small or genuinely absent. The positive associations between public nudity and body image appear to apply for those who identify as men, women, or neither.

Study 2 extended these findings by investigating three specific types of public nudity simultaneously: naturism, casual stripping, and sexting. In line with prior research (West, 2021) naturism predicted more body appreciation, and that this relationship was mediated by lower levels of social physique anxiety. Seemingly in contrast with prior research (Sherman & Hackathorn, 2020), casual stripping was also associated with positive outcomes: less social physique anxiety and (indirectly) more body appreciation. As in Study 1, these positive associations were not moderated by gender. Only sexting was associated with negative outcomes and this was the only association moderated by gender: sexting predicted more social physique anxiety in men (but not in women) and had no relationship with body appreciation. Below, we discuss these findings considering their implications, strengths and limitations, and suggestions for future research.

Implications

The positive effects of naturism on body image have been already documented in previous research (e.g., West, 2018, 2020, 2021). Nonetheless, these findings add to the generalisability of the relationship between naturism and body image. In particular, Study 1 used a very large sample of German participants, and Study 2 used a sample of mixed European participants. The consistency between these findings and prior research can increase our confidence about the positive effects of naturism, and the generalisability of these effects beyond a limited range of English-speaking countries.

Perhaps more surprising, these findings appear to contradict previous research which found that casual stripping was associated with negative (not positive) psychological factors (i.e., Sherman & Hackathorn, 2020). However, we can propose some potential reasons for these divergent findings. First, as mentioned before, Sherman and Hackathorn’s measure of casual stripping included items that could have applied to other forms of public nudity, making it unclear exactly what the scale was measuring. Second, Sherman and Hackathorn investigated different variables. Specifically, they found (1) associations between casual stripping and paternal neglect (which seemed to be a precursor and not consequence of casual stripping) and (2) associations between casual stripping and sociosexuality, a variable that can only be interpreted as negative if one holds a priori beliefs about the value of a woman’s modesty and sexual selectivity. It seems quite reasonable to interpret their findings differently, in line with prior research (e.g., Lewis & Janda, 1988) that found positive associations between nudity and comfort with one’s sexuality. In that light, it is also understandable that casual stripping may be similarly associated with lower levels of social physique anxiety and higher levels of body image in both men and women. In any case, research on stripping and psychological outcomes remains scarce and somewhat unclear, with some finding associations even between professional stripping and positive psychological outcomes (see, e.g., Sweet & Tewksbury, 2000; Wood, 2000). Thus, future research could be useful to clarify what the positive and negative effects of stripping may be.

Only one finding indicated associations between some form of public nudity and negative psychological outcomes (i.e., the association between sexting and social physique anxiety) and this finding only applied to men. While these findings do not go beyond prior research showing that sexting was sometimes associated with negative outcomes (Liong & Cheng, 2019), they do add meaningfully to these current findings in two ways. First, they clarify that not all forms of public nudity have similar associations with psychological outcomes; while naturism and casual stripping were associated with positive outcomes, sexting was associated with negative outcomes. Second, they undermine the simplistic interpretation of our findings that high levels of body image and low levels of anxiety about one’s body are necessarily the causes of more involvement in public nudity. At the very least, lower levels of anxiety about one’s body is associated with less frequent sexting (though more frequent naturism and casual stripping) suggesting that a more complex relationship exists between nudity and body image.

Finally, though this was not a central aspect of the study, it is noteworthy that a large proportion of the participants in both studies had engaged in some communal nude activity (Study 1 – 46%, Study 2 – 88% naturism, 62% casual stripping, 57% sexting). This suggests that willingness to take part in nude activity may be more widespread than it is often assumed to be.

Limitations and Future Research

These studies benefit from a number of strengths including theoretical replication across two studies, a very large sample size in Study 1, participants of varied nationalities, and participants who were more diverse than the widely overused student samples common in social psychology (Henrich, Heine, & Norenzayan, 2010). Practically, this research also provides a valuable tool for assessing body image in German-speaking countries by using the translation of the most recent version of the BAS-2, which has several advantages over the previous versions of the Body Appreciation Scale (Tylka & Wood-Barcalow, 2015a).

However, this research also has limitations. As both studies are cross-sectional, it is not possible to infer causal effects. Thus, a potential criticism is that this research merely shows that people who like their bodies are more likely participate in nudity. While it is plausible that a causal relationship exists in that direction, neither these current data nor prior research support the simplistic interpretation that this is the only causal relationship. As mentioned, this interpretation is incompatible with the finding that less anxiety about one’s body is associated with more of some forms of public nudity (naturism and casual stripping), but less of other forms (sexting). Furthermore, prior experimental research has shown a causal effect of public nudity on social physique anxiety and body image (West, 2021).

While the participants were diverse in some ways, most participants identified as White, and sexual orientation and cisgender or transgender status was not explicitly investigated. Also, despite the large samples, some amount of self-selection likely occurred, meaning that only participants were likely already interested in body image. Similar limitations found in other research on nudity and body image (West, 2018, 2020, 2021). Nonetheless, future research should specifically investigate whether the effects of public and communal nudity differ for participants who are not White, cisgender, and heterosexual.

We note that the effect size of the relationship between nude activity and body image in Study 1 was quite small. However, this could be due to the use of a relatively crude all-or-nothing measure of participation in nude activity; participants merely indicated (“yes” vs. “no”) whether they had ever taken part in such activity. Effect sizes were notably larger in Study 2, in which we used more nuanced measures. This further suggests that even more nuanced studies that include measures of how frequently, recently, or under what conditions participants took part in such activities may yield yet larger effect sizes, as well as more information about the ways to maximise the link between nudity and body appreciation.

Finally, though this research investigated specific, positive relationships between nude activities and body appreciation, future research should also continue to investigate the possible relationships between nude activity and negative outcomes. Several potential outcomes were not included in this research, such as body shame, body surveillance, overall life satisfaction, or even self-esteem. Including such outcomes may provide a more rounded picture of the positive and negative effects of all these activities.

Più povero è il linguaggio, meno esiste il pensiero

′′La graduale scomparsa dei tempi (congiuntivo, passato semplice, imperfetto, forme composte del futuro, participio passato…) dà luogo ad un pensiero al presente, limitato al momento, incapace di proiezioni nel tempo.

La generalizzazione del “tu”, la scomparsa delle maiuscole e della punteggiatura sono altrettanti colpi mortali portati alla sottigliezza dell'espressione.

Cancellare la parola ′′signorina′′ non solo è rinunciare all'estetica di una parola, ma anche promuovere l'idea che tra una bambina e una donna non c'è nulla.

Meno parole e meno verbi coniugati rappresentano inferiori capacità di esprimere le emozioni e meno possibilità di elaborare un pensiero.

[...]

Senza parole per costruire un ragionamento, il “pensiero complesso” caro a Edgar Morin è ostacolato, reso impossibile.

Più povero è il linguaggio, meno esiste il pensiero.

La storia è ricca di esempi e gli scritti sono molti da Georges Orwell in 1984 a Ray Bradbury in Fahrenheit 451 che hanno raccontato come le dittature di ogni obbedienza ostacolassero il pensiero riducendo e torcendo il numero e il significato delle parole .

Non c'è pensiero critico senza pensiero. E non c'è pensiero senza parole.

Come costruire un pensiero ipotetico-deduttivo senza avere il controllo del condizionale? Come prendere in considerazione il futuro senza coniugare il futuro? Come comprendere una contemporaneità o un susseguirsi di elementi nel tempo, siano essi passati o futuri, nonché la loro durata relativa, senza una lingua che distingua tra ciò che sarebbe potuto essere, ciò che è stato, ciò che è, cosa potrebbe accadere, e cosa sarà dopo ciò che potrebbe accadere? Se un grido dovesse farsi sentire oggi, sarebbe quello rivolto a genitori e insegnanti: fate parlare, leggere e scrivere i vostri figli, i vostri studenti.

Insegna e pratica la lingua nelle sue forme più svariate, anche se sembra complicata, soprattutto se complicata. Perché in questo sforzo c'è la libertà. Coloro che spiegano a lungo che bisogna semplificare l'ortografia, scontare la lingua dei suoi “difetti", abolire generi, tempi, sfumature, tutto ciò che crea complessità sono i becchini della mente umana. Non c'è libertà senza requisiti. Non c'è bellezza senza il pensiero della bellezza".

Cristoforo Clavé

People with a high conspiracy mentality tend to have relatively negative self-views; we don't know the causal link and maximum effect magnitude

Stasielowicz, Lukasz. 2022. “Core Self-evaluations and Conspiracy Mentality.” PsyArXiv. August 5. doi:10.31234/osf.io/sznc9

Abstract: There is mixed evidence of the relationship between conspiracy beliefs and self-appraisal constructs (self-esteem, self-efficacy, or neuroticism). However, in personality research, examining common elements of the three personality traits can be more useful than investigating traits separately. Therefore, the present study examined the relationship between core self-evaluations (CSE) and conspiracy mentality. Based on data of 596 participants, a small negative correlation was found using structural equation modeling (r = -.13, CR 95% [-.22, -.04]). People with a high conspiracy mentality tend to have relatively negative self-views. Future longitudinal studies could help clarify the causal link and maximum effect magnitude. 

Rise and Fall of Empires in the Industrial Era: A Story of Shifting Comparative Advantages

Rise and Fall of Empires in the Industrial Era: A Story of Shifting Comparative Advantages. Roberto Bonfatti & Kerem Coşar. NBER Working Papers 30295. July 2022. DOI 10.3386/w30295

Abstract: The last two centuries witnessed the rise and fall of empires. We construct a model which rationalises this in terms of the changing trade gains from empires. In the model, empires are arrangements that reduce trade cost between an industrial metropole and the agricultural periphery. During early industrialisation, the value of such bilateral trade increases, and so does the value of empires. As industrialisation diffuses, and as manufactures become more differentiated, trade becomes more multilateral and intra-industry, reducing the value of empires. Our results are consistent with long-term changes in income distribution and trade patterns, and with previous historical arguments.

IV Conclusions

“The Foreign and Colonial Offices are chiefly engaged in finding new markets and in defending old ones... Therefore, it is not too much to say that commerce is the greatest of all political interests, and that Government deserves most the popular approval which does the most to increase our trade and to settle it on a firm foundation.” (Joseph Chamberlain talking to the Birmingham Chamber of Commerce in 1896; cited by Ferguson 2004, p. 210)

“[in the mid 1950s] There were signs, particularly through the growth of intraindustry trade and the redirection of overseas investment, that the expansion of the international economy would take place increasingly between advanced economies. [...] Colonial trade, like colonial investment, was becoming less attractive. The pattern of specialisation that had promoted economic integration in the world economy since the nineteenth century was beginning to weaken, and the empires that were its political expression were losing their rationale.” (Hopkins 1997, p. 256).

In this paper, we have added to an otherwise standard trade model “empires” –institutional arrangements that reduce the cost of trading between an industrial center andbthe agricultural periphery. Using this model, we have shown that the emergence and later diffusion of industrialisation, as it occurred in the 19th and 20th century, can explain both the rise and fall of empires in the industrial era. In addition, increasing product differentiation may have further contributed to the demise of empires by incentivising intra-industry trade between developed countries. The above quotes, by prominent British historians, suggest that our model formalises arguments that have been in the historical literature for some time. A similar argument is made for France by Marseille (2015), who posits that French big business evolved from supporting the empire before World War I, to seeing it as a waste of money by the 1950s, largely due to its falling importance in world trade.

We finish with a discussion of how to interpret the model in light of historically relevant factors that we abstracted from. We haven’t allowed for the redistribution of the gains and costs from empire, neither between nor within locations. This suits our current purposes well, since a growing pie will make empires more sustainable, and a shrinking pie less so, however the pie is divided. A richer model, however, would accommodate factors such as coercion through military force, state capacity building and nationalism in the agricultural periphery, and cultural distances across locations. These were important factors in the history of empires. Military force also clearly evolved with industrialisation, since 19th century industrial products such as the Maxim gun gave the industrial centers a military lead which was perhaps comparable to that enjoyed by the first conquistadores in the 16th century.

Finally, the combined assumptions of imperfect specialisation, a spacious world, and lack of discriminatory trade policies against non-empire countries, shut off all strategic interactions amongst the industrial centers. If any of these assumptions is dropped, then to enlarge one’s empire will improve an industrial center’s terms of trade, to the detriment of all the others. This is the context in which competition amongst the industrial centers—such as the Scramble for Africa—could be studied.

Surveys: Continued coral recovery leads to 36-year highs across two-thirds of the Great Barrier Reef, but nothing is said of the average in the whole GBR

Annual Summary Report of Coral Reef Condition 2021/22: Continued coral recovery leads to 36-year highs across two-thirds of the Great Barrier Reef. Australian Institute of Marine Science, no date (YouTube movie dated Aug 3 2022.) https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2021-22

Summary: In 2022, the [Great Barrier Reef] continues to recover, registering the highest levels of coral cover yet recorded in the Northern and Central regions over the past 36 years (in the Southern part, recovery continued but hard coral cover declined slightly due predator's activity).

[...]

The recovery [...] continues to be driven by [vulnerable corals]. The [Barrier] remains exposed to the predicted consequencies of climate change. [...]. Any future disturbances can rapidly reverse the observed recovery.

Some comments:

1 you won't see the recovery in the news;

2 the AIMS doesn't publish _average_ coral cover since 2017, it only publishes data per region/area (Northern, Central, Southern Barrier);

3 the data above, if aggregated, would show record levels of coral cover since monitoring started for the whole, so, IMHO, it is misleading to say there is recovery in "two thirds of the Great Barrier Reef";

4 we are only monitoring the GBR since the mid-1980s, we don't know how were things before.

Now, why would the AIMS not publish aggregate cover since 2017? Critics think this may be due to a deliberate strategy of making things look worse than they are. Why would they do such a thing? Because of a linear combination of: they are true believers in the superior rights of Nature over us humans; they live off this (the taxpayer finances the surveys, the AIMS and several research positions at universities); the intimate satisfaction of being applauded by important bien-pensants; in a small number of persons, corruption; being good members of the herd; other reasons you may add.

I wrote to the AIMS asking them:

hi, thanks for your work. I got some questions about the reports on the Great Barrier Reef, like https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2021-22...:

1   what was the motivation to stop considering relevant the coral cover average, across all regions, which is no longer published (since, at least, 2017, as seen in "The whole GBR," https://www.aims.gov.au/reef-monitoring/gbr-condition-summary-2016-2017)?

2  are there papers in scientific publications about how good would it be to abandon publishing the cover average?;

3  does anyone knows what would be the result if the average were computed?; and

4  do they plan to start publishing again the average?

Once they reply I will post here their answer.

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Update Jul 31 2023: no reply until now

Across the first two decades of the 2000s, there is an increasing disinterest in becoming fathers among childless men

An increasing disinterest in fatherhood among childless men in the United States: A brief report. Robert Bozick. Journal of Marriage and Family, July 30 2022. https://doi.org/10.1111/jomf.12874

Abstract

Objective: The goal of this brief report is to document trends in expectations for and attitudes toward fatherhood among childless men across the first two decades of the 2000s.

Background: Childless men account for more than a third of adult men in the United States, but it is unclear if they desire to become fathers, and if not, whether this sentiment changed over time.

Method: Time trends for multiple measures of expectations for and attitudes toward fatherhood are plotted using samples of childless men from the National Survey of Family Growth, the Monitoring the Future study, and the Panel Study of Income Dynamics' Transition to Adulthood supplement.

Results: Across the time series, a growing share of childless men do not want children and increasingly, a lack of children would not bother them at all. Additionally, certainty in having children among childless men has waned over time and fewer childless men are concerned with parental leave policies when evaluating their job options.

Conclusion: Across the first two decades of the 2000s, there is an increasing disinterest in becoming fathers among childless men. These trends have broad implications for family researchers who study fertility rates, men's health, and family relationships.

Collective mental time travel: People have a more negative perception of the collective future than the personal future, maybe due to the press magnifying negative views

Collective mental time travel: Current research and future directions. Meymune N. Topcu, William Hirst. Progress in Brain Research, August 4 2022. https://doi.org/10.1016/bs.pbr.2022.06.002

Abstract: In this chapter, we will provide a review on the emerging psychological literature on collective mental time travel (MTT). Our review will focus on the cognitive aspects of remembering the collective past and imagining the collective future. We will explore factors such as specificity, phenomenal characteristics, content, and valence. We will also include brief overviews of cultural and social psychological research that is relevant to the topic of collective MTT. In these overviews, we will examine the research on narratives, collective continuity, collective angst, and human action. Three main themes will emerge from these discussions: the connection between collective past and future thinking, the differences between collective past and future thinking, and the role of goals, perceived agency, and collective action. We will integrate the findings of cognitive, cultural, and social psychological work through these three themes and offer ways to move collective MTT research forward.

Keywords: Collective memoryCollective future thinkingMental time travelValencePerceived agencyGoalsNarrativesCollective continuityCollective action

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people have a more negative perception of the collective future than the personal, maybe due to the press magnifying negative views

Check also: Topcu, M. N., & Hirst, W. (2020). Remembering a nation’s past to imagine its future: The role of event specificity, phenomenology, valence, and perceived agency. Journal of Experimental Psychology: Learning, Memory, and Cognition, 46(3), 563–579. https://doi.org/10.1037/xlm0000746

Abstract: People are routinely involved in remembering the national past and imagining the national future, especially when making political decisions. These processes, however, have not been explored extensively. The present research aims to address this lacuna. In 2 experiments (N = 203), participants were asked to remember and imagine events that involve the United States. Later, they rated these events in terms of phenomenal characteristics, valence, and perceived agency (circumstance, self, other-people, nation). Their responses were also coded for specificity and content. Past and future responses correlated for specificity, phenomenology, valence, and the four domains of perceived agency. Despite this strong correspondence between past and future thinking, there were also differences. Future responses were less specific and more positive than past responses. Moreover, people thought that they themselves and their nation will have more control over their nation’s future compared with the control they attributed to themselves and their nation over its past. The bias to be more optimistic about the nation’s future was partly explained by this tendency to see the nation as more agentic in the future. Taken together, these results reveal striking similarities and divergences between autobiographical and collective mental time travel. The present research provides an exploration for the newly emerging field of collective mental time travel. 

Why is exposure to opposing views aversive? Reconciling three theoretical perspectives.

Why is exposure to opposing views aversive? Reconciling three theoretical perspectives. Julia A. Minson, Charles A. Dorison. Current Opinion in Psychology, August 4 2022, 101435. https://doi.org/10.1016/j.copsyc.2022.101435

Abstract: To form truthful beliefs, individuals must expose themselves to varied viewpoints. And yet, people routinely avoid information that contradicts their prior beliefs—a tendency termed “selective exposure.” Why? Prior research theorizes that that exposure to opposing views triggers negative emotions; in turn, people avoid doing so. Here, we argue that understanding why individuals find simple exposure to opposing perspectives aversive is an important and largely unanswered psychological question. We review three streams of research that offer relevant theories: self-threat borne of cognitive dissonance; naïve realism (i.e., the illusion of personal objectivity); and reluctance to expend cognitive effort. While extant empirical research offers the strongest evidence for predictions from naïve realism, more systematic research is needed to reconcile these perspectives.

Environmental factors play a greater role in the etiology of psychotic experiences than genetic factors: some groups of individuals with seemingly low genetic risk for psychotic experience may develop them if exposed to high levels of environmental risk

Taylor MJ, Freeman D, Lundström S, Larsson H, Ronald A. Heritability of Psychotic Experiences in Adolescents and Interaction With Environmental Risk. JAMA Psychiatry. Published online August 03, 2022. doi:10.1001/jamapsychiatry.2022.1947

Key Points

Question  Are psychotic experiences less heritable for adolescents who experience more environmental risk factors?

Findings  In a twin study of 4855 twin pairs aged 16 years from the UK, the relative importance of genetic influences on certain psychotic experiences diminished with more exposure to environmental risk factors. A similar pattern of results was observed in an independent sample from Sweden (N = 8568 pairs).

Meaning  These results suggest gene-by-environment interactions in relation to psychotic experiences; some groups of individuals with seemingly low genetic risk for psychotic experience may develop them if exposed to high levels of environmental risk, in a similar manner to clinical observations in relation to schizophrenia.

Abstract

Importance  Genetic risk factors are known to play a role in the etiology of psychotic experiences in the general population. Little is known about whether these risk factors interact with environmental risks for psychotic experiences.

Objective  To assess etiological heterogeneity and exposure to environmental risks associated with psychotic experiences in adolescence using the twin design.

Design, Setting, and Participants  This twin study, conducted from December 1, 2014, to August 31, 2020, included a UK-based sample of twin pairs aged 16 years. This investigation evaluated the extent to which the genetic variance underlying psychotic experiences and the magnitude of the heritability of psychotic experiences was moderated by exposure to 5 environmental risk factors (bullying, dependent life events, cannabis use, tobacco use, and low birth weight). Psychotic experiences were assessed by 5 self-reported measures and 1 parent-reported measure. Participants’ exposure to environmental risks was assessed at birth and age 12 to 16 years. Structural equation models were used to assess differences in the variance in and heritability of psychotic experiences across these exposures, while controlling for gene-environment correlation effects. Analyses were repeated in an independent Swedish sample. Data analyses were performed from September 1, 2018, to August 31, 2020.

Main Outcomes and Measures  Primary outcome measures were exposure to environmental factors, as measured by a composite score, and psychotic experiences.

Results  A total of 4855 twin pairs (1926 female same-sex pairs, 1397 male same-sex pairs, and 1532 opposite-sex pairs) were included from the Twins Early Development Study (TEDS), and 6435 twin pairs (2358 female same-sex pairs, 1861 male same-sex pairs, and 2216 opposite-sex pairs) were included from the Child and Adolescent Twin Study in Sweden (CATSS). Mean age of twins from TEDS was 16.5 years. Mean age of twins from CATSS was 18.6 years. More exposure to environmental risk factors was associated with having more psychotic experiences. The relative contribution of genetic influences to psychotic experiences was lower with increasing environmental exposure for paranoia (44%; 95% CI, 33%-53% to 38%; 95% CI, 14%-58%), cognitive disorganization (47%; 95% CI, 38%-51% to 32%; 95% CI, 11%-45%), grandiosity (41%; 95% CI, 29%-52% to 32%; 95% CI, 9%-48%), and anhedonia (49%; 95% CI, 42%-53% to 37%; 95% CI, 15%-54%). This pattern was replicated for the measure of psychotic experiences in the independent Swedish replication sample. The heritability of hallucinations and parent-rated negative symptoms remained relatively constant.

Conclusions and Relevance  Findings of this twin study suggest that environmental factors play a greater role in the etiology of psychotic experiences than genetic factors. The relative importance of environmental factors is even higher among individuals exposed to environmental risks for psychotic experiences, highlighting the importance of a diathesis-stress or bioecological framework for understanding adolescent psychotic experiences.

Discussion

In this cohort study, we tested whether the heritability of adolescent psychotic experiences changes with exposure to environmental risks associated with psychotic experiences. Results suggest a gene-by-environment interaction for paranoia, hallucinations, cognitive disorganization, grandiosity, and anhedonia. The findings were replicated in an independent Swedish sample, thus lending robustness to our results. Our study thus suggests differences in heritability of certain psychotic experiences that may be associated with environmental exposures.

Specifically, there was an observed reduction in heritability of psychotic experiences in the presence of environmental exposures. These results are consistent with a bioecological framework, which would predict that more favorable environments would lead to higher heritability.²⁰Our results run contrary to a diathesis-stress pathway to psychotic experiences, which would predict that environmental risks trigger a genetic susceptibility to a given disorder and would thus lead to higher heritability of a phenotype in the presence of environmental risks.²⁰

It is also important to put our results in the context of prior studies of gene-by-environment interaction in relation to psychotic experiences. One study³³ reported that the association between environmental risks and psychotic experiences increased among individuals with a family history of psychosis. Although this finding also supports gene-by-environment interaction, the results are somewhat different than what would be expected from our analyses because our analyses suggest that genetic factors were less salient in the presence of environmental exposures. Moreover, other studies^34,35 have found no evidence of gene-by-environment interaction for psychotic experiences. Methodological differences may underlie these discrepancies. First, family history is not the same as genetic influence because family history includes a combination of genetic and shared environmental factors. Second, we focused on a composite exposure score comprising 5 environmental factors; prior studies have focused on more specific factors, including childhood physical abuse³⁵ and trauma.³⁴ Third, we focused on 6 specific psychotic experiences here, whereas prior studies used single measures. Finally, it is important to note that prior studies focus specifically on the interaction between genetic risk for psychotic experiences based on family history, by contrast with the current study that used the twin design. In our study, we tested whether heritability differed dependent on exposure to environmental risks. Heritability is a population statistic, and as such, an approach based on calculating heritability is somewhat different from an approach based on using family history as a proxy for individual genetic risk.

On a clinical level, it is first important to clarify that we focused on a young sample, who were aged 16 or 18 years. Many of these individuals will be too young to have been diagnosed with a psychotic disorder, but it is known that psychotic experiences in this age group can lead to severe clinical conditions in some individuals. Nonetheless, clinically it is often noted that many individuals with schizophrenia do not have a family history of schizophrenia. Indeed, although the relative risk for schizophrenia is increased among relatives of individuals diagnosed with schizophrenia, most relatives of individuals with schizophrenia do not develop schizophrenia.³⁶ Our results extend these observations to adolescent psychotic experiences and indicate that they may develop in a variety of contexts. Specifically, our results suggest that psychotic experiences may be prevalent in populations with a high degree of exposure to environmental risks associated with psychotic experiences. Indeed, there is substantial conjecture that psychotic experiences can be reached through multiple pathways, such as pathways that are more based on genetic propensity and others that are more down to environmental risks; however, to our knowledge, this is one of the first studies to provide replicable empirical findings on this topic.

The previously mentioned arguments should be tempered, however, for certain types of psychotic experiences. Although we observed that the heritability differed according to environmental exposure for some psychotic experiences, the heritability was more consistent for hallucinations and negative symptoms. This is important from a clinical perspective, given that negative symptoms are thought to be particularly predictive of subsequent mental illness. As such, these results lend further weight to the argument that the etiology of psychotic experiences may differ according to specific subtypes of psychotic experience.⁸

Strengths and Limitations

Strengths of our study included the use of 2 representative, population-based samples in different countries. In 1 sample, we measured 6 different specific psychotic experiences, enabling us to consider gene-by-environment interactions for different psychotic experiences. There were several limitations, however. Although we employed data from both the UK and Sweden, we still only focused on 2 European countries. Many of our exposures may differ in prevalence across the world, and it would therefore be useful to assess whether similar results emerge in countries with more environmental variability than the UK and Sweden. Our measures of tobacco and cannabis use were more brief than our other measures. Future studies should use more detailed measures. We also created a composite score that involved counting the number of exposures each participant had undergone, which included summing exposures that may have different etiologies or mechanisms underlying their association with psychotic experiences. Further, although our model has controlled for gene environment correlation, we recognize that birth weight is a complex phenotype influenced by parent and child genetics and prenatal environment.

It is further important to be aware that the environmental composite is not identical across TEDS and CATSS. The life events scale, for example, includes items about increasing numbers of quarrels with parents in CATSS, which are not covered in TEDS. Percentile-based cutoffs were used to define low birth weight; birth weight was lower in TEDS than CATSS on average, and therefore, this led to heavier twins being captured in CATSS. Exclusion criteria also differed between samples; individuals with extreme obstetric complications were excluded from TEDS but not CATSS. The fact that we observed similar results between CATSS and TEDS gives us confidence that these differences did not strongly influence our results; however, they should nevertheless be interpreted with these differences in measure in mind. Finally, twins are generally born lighter than singletons. We included birth weight as an exposure here, and hence, individuals with very low birth weight may have been overrepresented in our sample. However, studying birth weight in twins here is unlikely to create any issues for generalizability for 2 reasons. First, our modeling analyses were focused on variance rather than mean differences. Second, twins were compared with twins in the design (not singletons); as such, modest mean differences between singletons and twins in birth weight did not affect the findings.